It is estimated that almost 75,000 persons each year will die of acute respiratory insufficiency caused by lung disease alone. To address this problem, extracorporeal membrane oxygenation (ECMO) is used to provide external pumping and membrane oxygenation to assist the weakened or failing heart. Heat exchangers in the extracorporeal circulation (ECC) path are necessary to prevent water loss associated with evaporative heat loss in long term ECMO. Here, a short path length is particularly desirable to minimize the trauma to blood components coming contact with foreign surfaces. Heat exchangers can also be used to solve the problem of hypothermia and its associated coagulopathy occurring with trauma, the leading cause of death in young Americans. A small, portable unit used in line where blood and fluid are given could be utilized as early as the pre-hospital phase of support to prevent hypothermia. A microwave transmitter (heater) system is proposed to address problems associated with long term blood warming for ECMO and short term, rapid warming for trauma. This system would be small, portable and provide for a short ECC path. In addition, a closed loop temperature control system is possible by combining a passive, noninvasive microwave thermometry system with the transmitter.